This invention relates to a continuous process for the production of organic mono- or poly-isocyanates by continuous phosgenation of the primary amines on which the isocyanates are based.
It is known that organic isocyanates can be produced continuously by reacting primary amines with phosgene at elevated temperature and pressure. In German Offenlegungsschrift No. 2,252,068, e.g., production of isocyanates at super atmospheric pressures is described. In this process, the required isocyanate is used as solvent for the phosgene required. In German Auslegeschrift No. 1,768,439, a process in which amine solution is reacted with pure phosgene under similar temperature and pressure conditions is disclosed. And in German Offenlegungsschrift No. 2,404,773, primary amines are reacted with phosgene under pressure in the absence of solvents, (i.e., phosgene acts as the solvent).
Since the reaction of a primary amine with phosgene is an extremely fast reaction, the degree of mixing of these materials has a direct effect upon the reaction time and upon the yield of isocyanate. Methods of combining these two reaction components have therefore been investigated by those in the art. U.S. Pat. No. 3,781,320, for example, describes a special annular-gap mixer for combining these materials. French Pat. No. 7,628,343 describes a mixer which imparts a circulating and oppositely directed movement to the flow of at least one component. A process for mixing two liquids (particularly an amine with a phosgene solution), in which fan-shaped jets are used, is described in German Offenlegungsschrift No. 2,950,216; and German Offenlegungsschrift No. 1,792,660 describes an apparatus for mixing two streams of liquid reactants in which the streams are combined at an acute angle.